<?php
/**
 * 单例模式
 *
 * 保证一个类仅有一个实例,并提供一个访问它的全局访问点
 *
 */
 class Singleton
 {
     static private $_instance = null;

     private function __construct()
     {
     }

     static public function getInstance()
     {
         if(is_null(self::$_instance)) {
             self::$_instance = new Singleton();
         }
         return self::$_instance;
     }

     public function display()
     {
         echo "it is a singlton class function";
     }
 }

 // $obj = new Singleton(); // 声明不能成功
$obj = Singleton::getInstance();
var_dump($obj);
$obj->display();

$obj1 = Singleton::getInstance();
var_dump(($obj === $obj1));